1. Technical Field
The present invention relates to a method and apparatus for repairing and improving the endurance characteristics of process damaged oxide film formed in a semiconductor device and, more particularly, to sonic annealing by vibrating or oscillating a wafer at a predetermined frequency, wave amplitude, and exposure duration to bring about annealing of the gate oxide.
2. Description of Related Art
An unfortunate consequence of many different process methods for the fabrication of certain submicron devices, including the dry etching process, ion implantation process, and the plasma chemical vapor deposition (CVD) process, is the resulting damage of the thin gate oxide film of the device. This damage impacts the yield and reliability of complementary metal-oxide semiconductor (CMOS) transistors. By way of example, the ion implantation process refers to a mechanism of doping a semiconductor by means of ion implantation. The dopant atoms first are ionized so that each has a positive charge. Through the use of electric and magnetic fields the ions are focused into a well defined beam and accelerated to very high energies in a vacuum. The beam is then scanned into the surface of the wafer. This ion implantation method causes radiation damage to the substrate. This damage degrades carrier mobility and lifetime if not restored.
The silicon industry standard method for addressing the problem of such process induced damage is a high-temperature anneal after gate oxide growth within a single furnace cycle. This thermal annealing provides sufficient thermal energy to promote rearrangement of the atoms in oxide layer and, thus, repair of the damaged layer. A temperature range of 450xc2x0 to 1,000xc2x0 C. and heating cycle of about thirty minutes is typical for the high-temperature annealing process. These temperature ranges, however, are problematic for many submicron devices, such as a metal oxide semiconductor field effect transistor (MOSFET) device having a gate oxide thickness scaled below 100 xc3x85. The allowable thermal budget for these submicron devices becomes a constraint in light of the potential to otherwise permanently damage the device. As a result, annealing temperatures are typically reduced and only part of the damage caused by the initial process can be repaired by annealing. In addition, after forming an aluminum wiring film on the device, damage inflicted by the passivating process can not be subjected to high-temperature annealing due to aluminum""s low melting point. Since the damage that remains in these instances in the gate oxide is not ignorable in view of the reliability requirements of submicron MOSFET devices, a more effective method for treating the initial wafer processing induced damage, without the potential collateral affects of high-temperature annealing, is needed.
A method and apparatus for annealing oxide film is shown in which a wafer is vibrated or oscillated at a predetermined frequency and amplitude for a predetermined time period in order to anneal the gate oxide. This annealing process may be accomplished with a sonic wave device frequency generator in direct contact with the wafer, or a sonic wave anneal through a medium, such as air or a specific gas. In addition, the sonic wave anneal process could take place in situ during the oxide growing process with or without the contact described above. The oscillation frequency and amplitude, preferred medium, exposure time length, and medium temperature and pressure of the process can vary depending on the physical properties of the treated wafer and desired anneal. However, the method is preferred in lower temperature ranges in order to avoid the problems induced by typical high-temperature annealing.
Accordingly, it is a feature of the present invention to provide a method of repairing the damage induced by wafer processing within environmental parameters, particularly lower temperatures, that will not expose the device to the potentially damaging side effects that result from high temperature annealing. Another feature of the invention is to provide an alternative annealing process to the present industry standard high temperature annealing process. This alternative annealing process involves sonic annealing of the wafer by way of vibrating or oscillating the wafer at a predetermined frequency, amplitude, and time period in order to bring about an effective and efficient annealing of the gate oxide. The sonic annealing process of this invention may be utilized in a broad application of the manufacturing of semiconductor devices to improve the quality of, among other materials, BPSG and thin metal films.
The above as well as additional features and advantages of the present invention will become apparent in the following detailed written description.